Effective topical pre-exposure prophylaxis (PrEP) using antiretrovirals (ARVs) depends on the interception of HIV virions at the portal of entry during sexual exposure. Recent microbicide clinical trial results underscore the need for a more complete understanding of the pharmacological and cellular events that promote HIV prevention. Accordingly, this project will study the spatiotemporal distribution of ARVs following zero-order delivery from intravaginal rings (IVRs), as well as the co-localization with HIV and CD4-F immune cells following vaginal exposure to fluorescently labeled HIV virions in pig-tailed macaques (PTM). This application addresses a series of objectives that will couple ARV eluting device design to a deeper quantitative and qualitative understanding of the biodistribution of four ARV drugs: tenofovir disoproxil fumarate (TDF) and GS7340, potent prodrugs of tenofovir (TFV), the pyrimidinedione NNRTI/entry inhibitor IQP-0528, and the CCR5 entry inhibitor maraviroc (MVC). In aim 1, we will design and fabricate macaque-sized single agent IVRs for the controlled delivery of each of the ARVs described above to be used in PTM biodistribution studies in aim 2. We also will develop and evaluate human-sized IVRs for simultaneous delivery of a TFV prodrug with either MVC or IQP-0528. In aim 2, we will perform rigorous biodistribution studies in PTM and evaluate ARV concentration as a function of both longitudinal position in the vaginal tract and radial depth into the tissue following administration from IVRs produced in aim 1. In addition, we will expose the vaginal tract to fluorescently-labeled HIV and assess the distribution of both HIV virions and CD4+ immunocytes. In aim 3 we will construct mechanistic models that quantitatively describe ARV transport upon elution from IVRs and the distribution of HIV virions upon vaginal exposure to HIV infected semen. We will attempt to optimize and validate these models upon comparison with experimental data generated in aim 2 and use the resulting models to assist in the rational design of potentially efficacious dual-segment IVRs in aim 1.